This invention relates to axle assemblies for over-the-road vehicles such as trucks and, in one aspect, to self-steering axle assemblies which can serve either as primary axle assemblies or auxiliary axle assemblies for providing an additional load bearing axle when required to meet highway regulations.
Auxiliary axle assemblies are commonly used for load distribution purposes on trucks for hauling heavy loads, both tractor-trailer combinations and trucks. When deadheading, hauling a light load or a tractor is driven alone, such auxiliary axle assemblies typically are arranged so that they can be raised out of contact with the ground to eliminate unnecessary tire wear.
In many instances, the applicable government regulations require the auxiliary axle to be spaced some distance from the rear or drive wheels. Such spacing can cause a lateral slippage or tire scuffing when curves or corners are being negotiated. This problem can be minimized by making the auxiliary axle wheels steerable, such as by mounting the wheels on king pin assemblies and connecting the king pin assemblies together with a tie rod or the like so that the wheels turn together. Prior auxiliary axle assembly constructions including such an arrangement are exemplified in Lange U.S. Pat. No. 4,373,738 and Buelow U.S. Pat. No. 3,704,896.
Prior steerable axle assemblies tend to turn in the wrong direction during vehicle backing. For axle assemblies located in front of the vehicle drive wheels, the wheels tend to become turned to the left when the vehicle is being backed with the front wheels turned to the right and vice versa. For auxiliary axle assemblies located behind the vehicle drive wheels, the wheels tend to become turned in the same direction as the front wheels during backing, instead of following the rear wheels. Consequently, the auxiliary axle should be raised to avoid tire scuffing.
Lange U.S. Pat. No. 4,373,738 discloses connecting the auxiliary axle with the vehicle front wheels through a fluid-actuator system which is operable to steer the auxiliary axle wheels in response to steering movement of the vehicle front wheels. Such an arrangement is quite complex and unreliable.
Semi-truck tractors and some trucks, such as concrete-mixer trucks, commonly have tandem drive axles. The turning axle for such tractors and trucks typically is at the mid point of one axle or at a location between the axles. Consequently, when negotiating a curve or turning a corner, the tires on one or both of the axles slip sideways, causing scuffing.